1. Field of the Invention
The present invention relates to a method of manufacturing a molding of resin in which a large number of primarily formed resin moldings are secondarily formed at the same time and a passage for injecting resin material is heated, before the resin material is injected, in the process of secondary forming. The present invention also relates to a change-over device for changing over between the heating medium and the resin material in the process of secondary forming.
2. Description of the Related Art
When a hollow resin molding is manufactured and, for example, when an intake manifold for vehicle use is manufactured, it is common that the intake manifold is worked by secondary forming after primary forming has been completed. In this case, the manufacturing process is executed as follows. A primary molding, which has been manufactured to be divided into a plurality of pieces in the process of primary forming, is set in a mold used for secondary forming. Then, the divided primary moldings are butted to each other, and a passage for resin material is formed in the joint portion in which the divided primary moldings are butted to each other. When resin material used for secondary forming is injected into the passage, the intake manifold, which is a resin molding, can be integrally formed.
In the case where the resin molding is an intake manifold, the following problems have been encountered. As the passage formed in the primary molding is long, when secondary forming is conducted at the normal temperature on the primary molding which has already been cooled and solidified, the injected resin material used for secondary forming is quickly cured and the deposition property of the resin material is deteriorated. Accordingly, the deposition strength is lowered.
In order to solve the above problems and enhance the deposition strength, it is conventional to adopt a method in which resin material is injected after only the surface of the joint portion of the primary molding to be joined has been heated. This method is disclosed in the official gazette of JP-A-2003-245980.
According to this method, for example, the resin molding is an intake manifold, and a passage for injecting the resin material for secondary forming is formed in the joint portion of the primary molding, which is butted in the mold of secondary forming in the peripheries of the pipe portion and surge tank portion of the intake manifold. In one end portion of the intake manifold, for example, at one position in one portion of the surge tank, an inlet used for injecting a heating medium is provided. At the other end portion, for example, at an end portion of one pipe, one resin material injecting port is provided. When a heating medium is made to flow into the passage from the inlet used for injecting the resin material before the resin material is injected, the heating medium is sent onto the entire circumference of the passage so that the surface of the joint portion can be heated. After the heating medium has flowed onto the entire circumferential face of the passage, the flow of the heating medium is stopped, and the resin material for secondary forming is injected from the inlet into the thus heated passage.
Due to the foregoing, the primary molding, which has been divided into a plurality of pieces, can be joined by the uniformly heated resin material. Accordingly, the deposition strength can be prevented from being deteriorated.
However, in the forming machine described in the above patent document, the outlet of the heating medium is also used as an inlet of the resin material. Therefore, the temperature of the inlet of the resin is lowered by the heating medium in some cases. For example, when the temperature of the nozzle of the injection molding machine arranged at the inlet is lowered, the fluidity of the resin is deteriorated immediately after the start of injection.
Accordingly, it is desired to prevent the heating medium from flowing to the inlet of the resin material.
According to the method disclosed in the above patent document, as the passage for the resin material is long and, further, the outlet of the heating medium is also used as an inlet of the resin material, injection of the resin material for secondary forming, which is conducted after the heating medium has flowed into the passage, is delayed. When the injection time of injecting the resin material is delayed, even if the passage is heated, a portion of the injected resin material is cured before the other portions are cured, and the deposition property of the resin material is deteriorated and the deposition strength is lowered.
Therefore, it is desired that the resin material can be injected at a temperature in a uniform temperature range when a change-over cycle for changing over between the inflow of the heating medium and the injection of the resin material is shortened.
Especially when a large number of parts are secondarily formed, the injecting time of each part is different because the lengths of the joining portions of a plurality of primary moldings are different, that is, lengths of the flow of the resin are different. In this case, concerning the parts, the flow lengths of which are short, in order to prevent the resin material from overflowing, the injecting of the resin material into the parts must be finished while the resin material is being made to flow into the parts, the flow lengths of which are long. Therefore, it is necessary to provide a change-over device, which is different from the change-over device of the long passage, the flow length of which is long, in the short passage of the short flow length. In this case, it is necessary for the resin material not to be left in the change-over device at the time of releasing the mold. This is a problem to be solved.